can you explain more about what you mean by a "split track show"?
(if someone has a more coherent explanation, please share. Here's my attempt to explain...)
Each actor onstage has a track. Sometimes the track is just one character (Harold Hill). But usually the ensemble play more than one character (Jacey Squires in the Barbershop Quartet may also be one of the saleman on the train, a patron in the library, etc.) The specifics on each character he plays, where he enters/exits, his props, any set moves he performs, his costume changes are all part of the Jacey Squires "track".
In a split track show, you have more people out of a show than understudies/swings to cover the roles, so you have to split the actor tracks to make sure everything get covered. So Swing 1 may do a little of track A in one scene, then be track B in another scene, because those are the characters you need covered in those specific scenes. (Could also be referred to as a "cut show" because you are cutting characters/tracks from scenes because the swing can only be in so many places at one time.)
In our case we had Male Swing 1 covering tracks A & B while Male Swing 2 covered track C plus a couple parts of track B when A & B both HAD to be onstage together. And a female swing covered various parts of A & B when it didn't matter the sex (eg. a waiter became a waitress). We also cut tracks A & B if they weren't vital to the scene (eg. a patron in a club).
This then creates issues for wardrobe and hair (who is who when, where are they changing, who is their dresser for each change, a leisurely change is now quick, etc.) Issues for sound and micing (who is saying what lines, what lines are cut). Dance department (changing spacing to make up for holes in dance formations). Sometimes you can have the split tracks all worked out ahead of time as a precaution; but sometimes there are just so many ways that the chips can fall that it because impractical to have every permutation worked out before hand and you just have to create it on the day of.